Electric drive arrangement for internal combustion engines in motor vehicles

ABSTRACT

An electric drive arrangement for internal combustion engines in motor vehicles having an electric starter coupled to the internal combustion engine, and an electric generator drive connected with the internal combustion engine. The arrangement is connected to a supply battery via a semiconductor circuit arrangement, which determines the operation of the generator either in a generator mode or a motor mode. An electronic control device is used for controlling the starting operation of the internal combustion engine as a function of the signal of at least one temperature sensor with the aid of the generator operated as a motor, either alone or together with the starter. This arrangement makes it possible to achieve quicker and more comfortable starting operations in combination with lower pollutant emissions. The starting operations can be carried out reliably even at very low temperatures.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German Patent No. 19918513.1,filed Apr. 23, 1999, the disclosure of which is expressly incorporatedby reference herein.

The invention relates to an electric drive arrangement for internalcombustion engines in motor vehicles having an electric starter coupledto the internal combustion engine, and an electric generator driveconnected with the internal combustion engine.

For decades, internal combustion engines in road vehicles have beenstarted by means of an electronic starter which is connectedmechanically to the crankshaft of the internal combustion engine via itsstarter pinion and the ring gear on the flywheel only during thestarting phase. Nowadays, all starter motors have the torquecharacteristic of a series-wound machine, which is characterizedessentially by an output torque which falls continuously to zero as thespeed increases, beginning with the maximum possible torque atstandstill. During the starting operation this characteristic leads to atorque equilibrium between the starter torque and the drag torque of theinternal combustion engine at crankshaft speeds of between 80 and 200rpm, which are sufficient for starting according to the requirementswhich have applied hitherto. To make these starter motors as small,light and cheap as possible, d.c. machines of series-wound constructionor with permanent-magnetic excitation and as large as possible atransmission ratio relative to the crankshaft have been used. A totaltransmission ratio of the intermediate gear in the starter and thetransmission ratio of the starter pinion relative to the crankshaft isabout 60:1. This high transmission ratio necessitates an engagementdevice which establishes a driving connection with the crankshaft onlywhen the starter is actuated and hence protects the starter motor fromextreme speeds.

Future exhaust regulations will make the design of the above-describedstarting system inadequate. The minimum starting speeds hithertostipulated at the crankshaft lead to high pollutant emissions in thecurrent starting operation and it is known that there is considerablepotential for improvement in this area by raising the starting speed tovalues within the range of the idling speed of the internal combustionengine.

Another disadvantage of current starting systems is that startingoperations last a relatively long time and are relatively loud due tothe high transmission ratio of the starter relative to the crankshaftand the necessary engagement and disengagement of the starter pinion.This is becoming less and less acceptable to the customer, especially asfuture operating concepts for vehicles aimed at achieving fleetconsumption targets will require a significantly larger number ofstarting operations. This will result in problems with the life ofcurrent starting systems.

European Patent 0 793 013 A1 discloses a starting operation using abelt-driven generator instead of a conventional starter. Problems ariseat very low temperatures since the maximum torque of such an arrangementis no longer sufficient to start the engine reliably under suchcircumstances. Therefore such systems are restricted to internalcombustion engines with small displacements, at best. If a design forlarge internal combustion engines were implemented which also operatedreliably at low temperatures, this would lead to unacceptable large,heavy and expensive generators.

European Patent 0 406 182 B1 attempts to solve this problem by using aboost circuit to generate a higher voltage for starting, brieflybringing about higher currents in the generator—operated as a motor—andhence increasing torque. However, this solution has the disadvantagethat the belt drive loses adhesion at low temperatures and tends toslip. In addition, the charging time of the starting energy storage isdisruptive, thereby rendering it impossible to perform startingoperations is rapid succession. The life of such an arrangement isfurthermore inadequate for the future concepts, which necessitate alarge number of starting operations.

One object of the present invention is an economical electric drivearrangement for internal combustion engines which provides more rapidand more comfortable starting operation, and which also takes placereliably at low temperatures.

In particular, the drive arrangement according to the invention has theadvantage that, in combined operation, the driving torques of thegenerator and the starter are superimposed in an effective manner sincethe torque of the active generator cuts in precisely when the starterbegins to slacken off. The crankshaft of the internal combustion engineis thereby accelerated very rapidly to well beyond the speed that cancurrently be achieved by a starter, thus ensuring rapid and reliablestarting even at low temperatures. In the case of a cold start, adivision of tasks occurs between the conventional starter (overcomingthe break-away torque) and the generator (increasing the cranking torquein the range of higher crankshaft speeds). Over dimensioning of thegenerator together with the power electronics and an unwantedintervention in the drive line can be avoided, and a starter, can beused virtually unaltered. The solution according to the invention thusrepresents an optimum cost solution. At higher outside temperaturesand/or with a warm engine, the starting operation can be performedsolely with the generator, thereby enabling particularly comfortablestarting with particularly little noise. The electronic control deviceadvantageously decides the starting operation mode as a function of atleast on temperature sensor.

The semiconductor circuit to accomplish the present invention canadvantageously be connected as an inverter for motor operation of thegenerator, which is designed as an a.c. or d.c. generator, and as arectifier for generator operation, making it possible to use a singlesemiconductor circuit for both modes of operation, with a correspondingimprovement in efficiency by active rectification in the generator mode.

The decision as to whether the starting operation should be performedsolely by means of the generator operated as a motor or by means of thisgenerator in combination with the starter is made in an optimum mannerby the electronic control device as a function of the engine-oiltemperature and/or the outside temperature and/or the off time of theinternal combustion engine. To start the internal combustion engine atlow temperature, the generator and the starter can be switched onsimultaneously or in succession with or without a time overlap. Thesevariants can, for example, be chosen as alternatives depending on therespective starting parameters.

It is further advantageous that the electronic control device bedesigned to set a defined angular position of the crankshaft of theinternal combustion engine when switching the engine off with the aid ofthe generator, which is operated as a motor. For this purpose, thegenerator is, for example, designed as a fully functional four-quadrantpositioning drive. This allows the next starting operation to take placefrom a defined initial position, thereby considerably speeding up thestarting operation and considerably reducing pollutant emissions.Moreover, one of the hitherto customary sensors, either the TDC (TopDead Center) sensor or the camshaft sensor can be omitted. Activatingthe ignition and/or injection during the starting operation of theinternal combustion engine only at speeds close to the starting speed,e.g. at 80% of the starting speed is particularly favourable for lowenergy consumption and low pollutant emissions.

The electronic control device can also advantageously be used to supportdeceleration operations of the internal combustion engine by switchingon the generator, operated in the generator mode, and/or to assistacceleration operations of the internal combustion engine by switchingon the generator, which operated in the motor mode. For example,operation of the generator as a motor can be used to assist drivingdynamics while the internal combustion engine is running, i.e. as anintervention of the active generator for the purpose of assistanceduring all acceleration processes of the internal combustion engine. Onthe other hand, it is also possible for rotational energy of theinternal combustion engine to be recovered when the generator isoperated as a generator, especially in overrun and braking mode, withthe result that the generator additionally assists the desireddeceleration process. This mode selection takes place most efficientlyas a function of the speed of the internal combustion engine.

The active generator can also advantageously be involved insynchronizing the engine and gearbox speeds during gear changes inmanual gearboxes. The energy which has to be converted in thesynchronizer rings of the gearbox to equalize the rotational speeds canbe recovered by means of the generator, and, in addition, more rapidgear changes are obtained, possibly even eliminating the need forsynchronizer rings and a clutch, given appropriate design. During aprospective gear change, the engine is controlled in such a way with theassistance of the generator that no torque is transmitted in the driveline. The respective gear can then be disengaged. Re-equalization of thespeed then takes place with the aid of an electronic accelerator or withthe aid of an electronic throttle valve and electronic assistance. Whenthe engine speed has been synchronized with the new gearbox speed, nojerking movement occurs during the new gear engagement.

It is also possible to prevent excessive device belt slip between theinternal combustion engine and the generator by switching on generatoroperation of the generator or motor operation of the generator.Additional torques at the belt drive can thereby be connected anddisconnected or compensated for in a manner which spares the belt, thusincreasing the life of the drive belt and largely preventing defects.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of an internal combustion engineprovided with a starter and an electric generator and

FIG. 2 shows a diagram to illustrate the mode of operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the exemplary embodiment illustrated in FIG. 1, a schematicallyrepresented internal combustion engine 10 of a motor vehicle is providedwith a starter 11 and an electric generator 12, the electric generator12 being coupled to the internal combustion engine 10 by a (not shown)belt drive.

The starter 11 is connected directly to a supply battery 14, and theelectric generator 12 is connected to the battery via a semiconductorcircuit arrangement 13.

An electronic control device 15 controls the starter 11 and thesemiconductor circuit arrangement 13 as a function of sensor signals andstart control signals which the control device 15 obtains by means of astarter switch 16, which can be integrated into the ignition lock and/ordesigned as a separate starter switch. In the exemplary embodiment, thecontrol device 15 is supplied with sensor signals by an externaltemperature sensor 17, an oil temperature sensor 18 and an intake-pipepressure sensor 19. However, the control device 15 can, in addition, besupplied with, for example, sensor signals which are dependent on thebattery load state, the battery voltage, the current of the battery andthe on-board electrical system, the engine speed, pedal positions orparameter switches.

Depending on the operating condition, the semiconductor circuitarrangement 13 receives control signals, from the control device 15, formotor (active) or generator operation of the generator 12. For generatoroperation, the semiconductor switch arrangement 13 is connected as arectifier or rectifier bridge while, for motor operation, the switch isconnected as an inverter for the generator 12 designed as an a.c. ord.c. generator.

In response to a starting signal from the starter switch 16, theelectronic control device 15 activates the starter 11 and connects thesemiconductor circuit arrangement 13 as an inverter. As a result, thestarter 11 and the generator 12 perform the starting operation of theinternal combustion engine 10 jointly. FIG. 2 shows the torques and themechanical power of the starter 11 and the generator 12 at thecrankshaft, the solid lines representing the torques and the brokenlines the powers as a function of the crankshaft speed. Thisillustration shows that the initially high torque of the starter fallsrapidly and continuously to vanishingly small values as the rotationalspeed increases, and the initially increasing power likewise falls beloweven 300 rpm, to a value of essentially zero. In contrast, the torque ofthe generator 12 is constant and the power rises in an essentiallylinear manner. The diagram thus shows that the torque of the activegenerator cuts in precisely when that of the starter begins to slackenoff. The superimposition of the two driving torques takes effect at thecrankshaft and accelerates it well beyond the speed that can be achievednowadays with a starter.

This combined operation is necessary particularly in the case of a coldstart and low outside temperatures since the conventional starter 11 hasan initially very high driving torque which is effective even at lowtemperatures.

When the internal combustion engine 10 is warm or the outsidetemperatures are high, only the electric generator 12 is required forthe starting operation. Thus, the semiconductor circuit arrangement 13is accordingly merely connected as an inverter to provide motoroperation of the generator 12.

These two different starting processes, i.e. cold starting and warmstarting, are stored as an algorithm in the control device 15 as afunction of corresponding sensor signals. For example, a cold start canbe defined by the engine-oil temperature and the outside temperaturebeing below a predeterminable value and/or by the off time since thelast operation of the internal combustion engine being greater than apredeterminable time period. A warm start is defined engine-oiltemperatures and outside temperatures above definable values and/or atoff times smaller than a predeterminable time period. It is alsopossible for the relationship between these sensor variables to bedefined by a particular function.

For cold starting, two different starting methods can be implemented. Inone starting method, the generator operates as a motor in parallel withthe starter 11. In this case, the starter is deactivated at a certainspeed and the generator, operating as a motor, accelerates thecrankshaft further to the starting speed.

In the second variant, the starter 11 is switched on first and only whena certain speed has been reached is it deactivated and the generator,operated as a motor, is activated. To lower consumption and reducenoxious exhaust gases, no injection and no ignition are carried outuntil a speed value corresponding, for example, to 80% of the startingspeed is reached, and the internal combustion engine 10 is thus onlystarted at this point. This starting operation takes place very rapidlyby means of an electronic engine control system (not shown), which canbe operatively connected to the electronic control device 15. Thisdelayed onset of ignition and injection also takes place in acorresponding manner in the case of a starting operation solely by meansof the generator 12.

Customary starters 11 have a total transmission ratio of about 60:1,this being obtained from the transmission ratio of the starter pinion tothe crankshaft and by the intermediate-gear transmission ratio. In thearrangement according to the invention, this transmission ratio can besignificantly reduced. That is, the intermediate gear can, for example,be omitted, thus giving a total transmission ratio of 15:1.

Independently of the starting operation, the electronic control device15 can also control the generator 12 to assist with driving dynamics,for example, while the internal combustion engine 10 is running. In allacceleration operations of the internal combustion engine 10, forexample, the generator 12—operated as a motor—can assist theseacceleration operations. On the other hand, it can also assistdeceleration operations in generator mode, i.e. it is operated as agenerator in overrun mode and braking mode, with the result that notonly is electric energy recovered, depending on the driving situation,but the deceleration process is also actively assisted.

The electronic control device 15 can furthermore actively assist shiftoperations during gear changing in the gearbox of the internalcombustion engine 10 and be used to synchronize engine and gearboxspeeds. To increase the speed, the generator 12 is operated as a motorand to reduce the speed the generator 12 is operated as a generator.This leads to faster gear changes, thereby making it possible to omiteven a clutch under certain circumstances.

The electronic control device 15 can furthermore be used to prevent beltslip of the generator 12. A measuring device (not shown) for detectingbelt slip transmits its measurement signals to the electronic controldevice 15, which uses the active generator 12 to couple or decouple orcompensate, in a manner which reduces additional torque on the belt.This measurement device for detecting belt slip can also be part of theelectronic control device 15, where the speeds of the generator 12 andthe internal combustion engine 10 are compared with one another. Forbelt slip detection, it is possible, for example, for a measurementroller to be resiliently and pivotally connected to the forward strandand the return strand of the drive belt, these measurement rollersdetecting the stretching of the drive belt due to different torques.Detection of the belt slip allows preventive belt diagnosis and the riskof a problem with the belt can be communicated to the driver of a motorvehicle at an early stage, e.g. by means of an optical and/or acousticwarning device or a display.

The electronic control device 15 can furthermore be used to position thecrankshaft. When the internal combustion engine is switched off, afavourable well-defined initial position is imposed on the crankshaft bythe generator 12, which is operated as a motor. For this purpose, thegenerator is, for example, designed as a fully functional four-quadrantpositioning drive. As a result, the next starting operation of theinternal combustion engine can be performed from a defined initialposition, thereby considerably speeding up the starting operation.

The arrangement according to the invention is also suitable forcontrolling or influencing the running down of the internal combustionengine 10. Undefined quantities of fuel often remain in the intakesystem and the cylinders when the internal combustion engine 10 isswitched off. The highly volatile components of the fuel evaporate,however, the poorly combustible components do not evaporate. They impairthe quality of the exhaust gas when the internal combustion engine isrestarted. This problem is circumvented in a refinement of the inventionby switching off the fuel supply or fuel injection when the internalcombustion engine 10 is switched off. The revolution of the internalcombustion engine 10 is maintained for a certain time by the generator12 in motor mode, thereby flushing the internal combustion engine andharmlessly disposing of fuel residues, which may also be in thecatalytic converter. When the internal combustion engine is restarted,the engine control unit or control device 15 can assume that theinternal combustion engine is “empty” and this makes a defined starteasier.

After flushing and the disposal of the fuel residues, the internalcombustion engine 10 can be braked to a halt in a defined manner withthe generator 12 in generator mode since a long after-running phase isnot desirable.

Another application of the drive arrangement according to the inventionis the improvement of the start/stop operations of the internalcombustion engine 10, e.g. at traffic lights. Opportunities forimplementation increase especially if the internal combustion engine ormotor vehicle can be started without delay. Even the slightest delaysare viewed by an operator as being extremely irritating. With the aid ofthe electronic control device 15 in conjunction with the generator 12,it is possible to stop the vehicle without disconnecting the internalcombustion engine. Any other torque shocks which occur can becompensated for by the generator in a comfortable manner. Starting isthen likewise performed once more without operating a clutch, by“electrical” drive-away, this being possible completely without a delay.This can, of course, also be performed with the internal combustionengine disconnected. In motor operation of the generator 12, purelyelectrical drive-away may take place with assistance from the starter11, particularly when the internal combustion engine is cold ortemperatures are very low. The starting or connection of the internalcombustion engine 10 can then be performed with something of a timedelay, in particular in a pulsed manner. Since, during starting of theinternal combustion engine, the vehicle is then already in motion, thekinetic energy of the entire vehicle, not just individual parts of thedrive line, is involved in starting the internal combustion engine, thusensuring reliable starting.

Such a start/stop system preferably operates in connection with aroad-condition detection system, such as an electronic stabilizationsystem or traction control system.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. An electric drive system for an internalcombustion engine in a motor vehicle having an electric starter for theinternal combustion engine, an electric generator in drive connectionwith the internal combustion and a battery for supplying voltage, saidsystem comprising: a semiconductor circuit connected to said battery andsaid generator; and an electronic control device controlling saidsemiconductor circuit, said electronic control device having a firstinput for receiving a vehicle start signal, a second input for receivingat least one temperature sensor signal and at least one output forproviding a control signal to said electric starter and saidsemiconductor circuit; wherein said electronic control device outputsignal controls on and off operation of said electric starter andcontrols said semiconductor circuit to effect operation of saidgenerator in either a motor mode or a generator mode; whereby startingof said internal combustion engine is performed as a function of saidgenerator operating as a motor either alone or together with saidelectric starter, wherein said electronic control device includes meansfor switching the generator to operate as a motor, after the internalcombustion engine is switched off and the fuel supply is switched off inorder to maintain the rotation of the internal combustion engine duringa post-operative phase until all residues still contained in theinternal combustion engine or in a catalytic converter have beensubstantially removed.
 2. The system according to claim 1, wherein saidsemiconductor circuit is connected as an inverter for motor operation ofthe generator, and is connected as a rectifier for operating in agenerator mode in which said generator is an a.c. or d.c. generator. 3.The system according to claim 1, wherein the starting operation iscontrolled as a function of at least one of an engine-oil temperatureand the off time of the internal combustion engine.
 4. The systemaccording to claim 1, wherein said electronic control device outputssaid at least one control signal to start the internal combustion engineby means of the generator and the starter when said at least onetemperature input signal is less than a predetermined value, and tostart the internal combustion engine by means of the generator alonewhen said at least one temperature input signal is above saidpredetermined value.
 5. The system according to claim 4, wherein saidoutput control signals from said internal combustion engine function tostart the internal combustion engine when said input temperature isbelow a predetermined value such that the generator and starter areswitched-on on one of simultaneously and successively with or without atime overlap.
 6. An electric drive system for an internal combustionengine in a motor vehicle having an electric starter for the internalcombustion engine, an electric generator in drive connection with theinternal combustion and a battery for supplying voltage, said systemcomprising: a semiconductor circuit connected to said battery and saidgenerator; and an electronic control device controlling saidsemiconductor circuit, said electronic control device having a firstinput for receiving a vehicle start signal, a second input for receivingat least one temperature sensor signal and at least one output forproviding a control signal to said electric starter and saidsemiconductor circuit; wherein said electronic control device outputsignal controls on and off operation of said electric starter andcontrols said semiconductor circuit to effect operation of saidgenerator in either a motor mode or a generator mode; whereby startingof said internal combustion engine is performed as a function of saidgenerator operating as a motor either alone or together with saidelectric starter, further including a crankshaft control output fromsaid electronic control device to set a defined angular position of thecrankshaft when the internal combustion engine is shut off.
 7. Anelectric drive system for an internal combustion engine in a motorvehicle having an electric starter for the internal combustion engine,an electric generator in drive connection with the internal combustionand a battery for supplying voltage, said system comprising: asemiconductor circuit connected to said battery and said generator; andan electronic control device controlling said semiconductor circuit,said electronic control device having a first input for receiving avehicle start signal, a second input for receiving at least onetemperature sensor signal and at least one output for providing acontrol signal to said electric starter and said semiconductor circuit;wherein said electronic control device output signal controls on and offoperation of said electric starter and controls said semiconductorcircuit to effect operation of said generator in either a motor mode ora generator mode; whereby starting of said internal combustion engine isperformed as a function of said generator operating as a motor eitheralone or together with said electric starter, further including meansfor activating an ignition during the starting operation of the internalcombustion engine providing speeds substantially equal to the startingspeed.
 8. The system according to claim 1, further including means foractivating the ignition during the starting operation of the internalcombustion engine providing speeds only at speeds which are close to thestarting speed, wherein, during operation of the engine, the electroniccontrol device outputs a deceleration signal to switch on the generatorin the generator mode and wherein said electronic control deviceprovides an acceleration signal to assist acceleration operation of theinternal combustion engine by switching the generator to operation as amotor.
 9. The system according to claim 8, wherein the switching-on ofthe generator in the generator mode is accomplished as a function of thespeed of the internal combustion engine.
 10. The system according toclaim 8, wherein the switching-on of the generator as one of a generatormode or a motor mode is accomplished to provide synchronization of theengine speed and the gearbox speed during gear changing.
 11. The systemaccording to one of claim 8, wherein the switching-on of the generatorin the generator mode or in the motor mode compensates for differenttorques at the belt drive of the generator.
 12. The system according toclaim 1, further including means for switching the generator fromoperation as a motor to operation as a generator after thepost-operative phase.
 13. An electric drive system for an internalcombustion engine in a motor vehicle having an electric starter for theinternal combustion engine, an electric generator in drive connectionwith the internal combustion and a battery for supplying voltage, saidsystem comprising: a semiconductor circuit connected to said battery andsaid generator; and an electronic control device controlling saidsemiconductor circuit, said electronic control device having a firstinput for receiving a vehicle start signal, a second input for receivingat least one temperature sensor signal and at least one output forproviding a control signal to said electric starter and saidsemiconductor circuit; wherein said electronic control device outputsignal controls on and off operation of said electric starter andcontrols said semiconductor circuit to effect operation of saidgenerator in either a motor mode or a generator mode; whereby startingof said internal combustion engine is performed as a function of saidgenerator operating as a motor either alone or together with saidelectric starter, wherein the electronic control device includes anoutput for controlling the starting operation of the internal combustionengine for immediate driving away of the motor by operation of thegenerator in the motor mode.
 14. The system according to claim 13,wherein starting of the internal combustion engine is delayed in thecase of an electronic driving away of the motor vehicle by means of thegenerator operated as a motor.
 15. An electric drive system for aninternal combustion engine in a motor vehicle having an electric starterfor the internal combustion engine, an electric generator in driveconnection with the internal combustion and a battery for supplyingvoltage, said system comprising: a semiconductor circuit connected tosaid battery and said generator; and an electronic control devicecontrolling said semiconductor circuit, said electronic control devicehaving a first input for receiving a vehicle start signal, a secondinput for receiving at least one temperature sensor signal and at leastone output for providing a control signal to said electric starter andsaid semiconductor circuit; wherein said electronic control deviceoutput signal controls on and off operation of said electric starter andcontrols said semiconductor circuit to effect operation of saidgenerator in either a motor mode or a generator mode; whereby startingof said internal combustion engine is performed as a function of saidgenerator operating as a motor either alone or together with saidelectric starter, wherein said electronic control device furtherincludes means for controlling the stopping operation of the motorvehicle without disconnecting internal combustion engine by means of thegenerator.